Handling Rust

Context

Rust has dependency on LLVM and we need a decision on how to handle it in the future. We need Rust internally for librsvg and g-b-m needs it for some things.

Description

Some options:

1. Just build LLVM for Rust and bundle it in our extension, keep updating extension as is
2. Keep building Rust in our runtime but stop exposing it. g-b-m will pull it through junction. Flathub will start building the Sdk extension.
3. Stop building Rust completely. Pull Rust through ostree element from Flathub.

Acceptance Criteria

There's a solid plan of how we can ensure Flathub Sdk extension actually keeps having new Rust.